Mobile networks are not stable channels. A subway passenger loses 30% of packets, switching from WiFi to LTE causes a 2–3 second break, an elevator ride means a full minute of no signal. Most apps are tested only on stable WiFi and perform catastrophically in the real world: spinning spinners, frozen forms, lost data. We offer professional testing of mobile apps under unstable internet. After such testing, user complaints drop by 60%, and post-release bug-fixing costs by up to 40%. Network simulation using modern tools helps uncover bugs before release and improves app fault tolerance.
Why Standard Tests Don't Show the Real Picture
Standard tests are conducted in lab conditions with an ideal network. But 90% of users experience connectivity issues daily. An app that works perfectly on a test bench may crash or freeze for customers. Simulating packet loss, delays, and network switching is mandatory for any serious project. We use tools that emulate real conditions: from Network Link Conditioner to tc on Android.
How to Simulate an Unstable Network
iOS: Network Link Conditioner
On iOS, the standard tool is Network Link Conditioner from Additional Tools for Xcode. It is installed on the simulator and real device via Settings → Developer. Profiles: 3G, Edge, 100% Loss, Very Bad Network (5% loss, 500ms delay). You can create custom ones: set Downlink Bandwidth, Uplink Bandwidth, Delay, Packet Loss. According to Apple's documentation, the tool accurately emulates different network types.
| Profile | Bandwidth (Down/Up) | Delay | Packet Loss |
|---|---|---|---|
| 3G | 1 Mbps / 512 Kbps | 200ms | 0% |
| Edge | 200 Kbps / 100 Kbps | 300ms | 1% |
| Very Bad Network | 500 Kbps / 250 Kbps | 500ms | 5% |
Programmatic control for automated tests is via XCTest and XCTNSURLSessionTaskMetrics. Metrics provide data on actual connection conditions.
Android: tc and Emulator Network Settings
On the emulator: Emulator Extended Controls → Cellular → Network type → Edge / GSM and Signal strength → Poor. Programmatic simulation via adb and tc (traffic control):
# Add 500ms delay and 20% packet loss adb shell tc qdisc add dev wlan0 root netem delay 500ms loss 20% # Reset adb shell tc qdisc del dev wlan0 root tc netem works at the network interface level of the emulator. On a real device, root is needed — for testing we use an emulator or real poor coverage zones.
Cross-Platform: Charles Proxy and Proxyman
Charles Proxy (macOS/Windows) and Proxyman (macOS) work as man-in-the-middle proxies. The app is configured to use the proxy, and throttling is applied: Charles → Proxy → Throttle Settings: profile GPRS / 3G / Custom. All requests go through the proxy with simulated delay. Additionally, Breakpoints: intercept a request, delay it by 10 seconds manually, simulate a timeout. Useful for checking UI in a waiting state.
How to Simulate Packet Loss on Android?
For this, use tc netem with the loss parameter. Example: adb shell tc qdisc add dev wlan0 root netem loss 15% sets 15% packet loss. This checks the app's reaction to partial disconnects. We recommend testing with loss from 5% to 30% for different scenarios.
What Do We Check and What Bugs Do We Find?
Timeout and Retry Logic
A request hangs for 30 seconds — what does the user see? A spinning spinner with no way to cancel is bad. A "Cancel" button + timeout + error message is good. We check each type of request.
Network Switching
Switching WiFi→LTE interrupts TCP connections. Correct behavior: the app detects the change via NWPathMonitor (iOS) or ConnectivityManager.NetworkCallback (Android) and reconnects. Incorrect: infinite spinner because the old URLSession task hangs.
Packet Loss
At 15–20% packet loss, an HTTP request may complete or hang. We verify: every request has a timeout (5–15 seconds for data, 30–60 for file uploads), and retry with exponential backoff.
Partial Loading
Data arrives in chunks on a slow connection. If the app shows content only after receiving the entire response, the user sees a white screen for 10 seconds. Streaming or progressive loading improves perception.
Typical bugs:
- Unclosed connections.
URLSessionwith tasks that are not canceled when the controller disappears. Consequence: memory leak + request after 30 seconds when the screen is already closed, crash withEXC_BAD_ACCESS. - Duplicate requests on retry. The "Retry" button calls the same method that is already running. Fix: an
isLoadingflag, disable the button. - Data loss on interruption. User fills a form, presses "Save", connection drops. Data is not saved. Solution: local draft save, automatic send on restoration.
Comparison of Simulation Tools
| Tool | Accuracy | Flexibility | Setup Complexity |
|---|---|---|---|
Network Link Conditioner |
High (system-level) | Medium | Low |
Android tc |
High (real delay) | High | Medium |
Charles Proxy |
Medium (depends on network) | High | Medium |
Proxyman |
Medium | High | Medium |
Network Link Conditioner is best for quick iOS tests, Charles Proxy allows complex scenarios with breakpoints. For Android, tc is indispensable for precise tuning.
What's Included
- Documentation: description of all tested scenarios and conditions.
- Video recording: every bug is recorded on video with annotations.
- Report: detailed analysis with recommendations for fixes.
- Training: consultation with the development team on found issues.
Process
- Analysis — we study the app architecture, identify critical requests.
- Configuration — select and configure simulation tools.
- Testing — run through a checklist of 25+ scenarios: packet loss, delays, network switching, timeouts.
- Bug capture — record video, logs, screenshots.
- Report — deliver a detailed report with recommendations.
- Consultation — discuss results with the development team.
Timeline and Pricing
Testing takes from 2 to 3 days depending on the app size. Pricing is individual and depends on the number of scenarios and architecture complexity. On average, our clients save up to 40% of the budget on post-release bug fixes. Contact us for a project assessment. Order testing — get a free consultation.